1. Field of the Invention
This disclosure relates generally to the field of hydrogen peroxide production. More specifically, this disclosure relates to methods and apparatus for the on-site and in-situ production of hydrogen peroxide.
2. Background of the Invention
Hydrogen peroxide (H2O2) has long been known as an antiseptic but has not been widely used for industrial sterilization largely due to cost. It also typically requires significantly higher dosage levels than chlorine for similar activity. In light of the tightening regulation of chlorinated compounds, however, this compound is being re-examined and is found to be quite effective in a number of industrial disinfection applications. Also, when indirect costs for factors such as corrosion, liability and insurance, and safety concerns are taken into account, the cost for treating with H2O2 is found to be very similar to that for the use of chlorine in the control of biofouling in powerplants, and in several Orange County, Calif. sewage treatment facilities. When employed to accomplish sterilization in these situations, H2O2 concentrations of 50-200 ppm are typically required for sufficient effectiveness although recent data suggests that as little as 2 ppm can be effective towards fouling control.
The main drawbacks to traditional (chemical) sources of hydrogen peroxide are cost and safety. Industrial bulk sources of concentrated hydrogen peroxide are currently produced by use of a catalyzed reaction cycle which entails reducing anthraquinone to anthrahydroquinone using hydrogen, followed by air oxidation back to anthraquinone. In this process, the oxygen is reduced to hydrogen peroxide. This approach does not permit pure hydrogen peroxide to be generated directly in liquid streams because the direct required contact between oxygen and anthrahydroquinone contaminates the hydrogen peroxide with the quinone and the products of its oxidation and degradation. Consequently, present industrially established methods for hydrogen peroxide production produce bulk quantities of the chemical which are subsequently shipped to, and stored by, the hydrogen peroxide user. This leads to substantial expenses for transportation and storage. On-site production of hydrogen peroxide in the liquid stream of concern would eliminate the time and expense of storage and transportation, as well as the associated hazards.
Concentrated chlorine is much less expensive to use, but has several disadvantages. First, strong chemicals must be manually handled and stored in concentrated form on site, posing an occupational hazard to workers. Generating cleansing solutions when needed at the proper concentrations on site would substantially reduce these hazards. Second, few membranes (especially NF and RO membranes) can tolerate significant levels of chlorine without degrading, whereas hydrogen peroxide has better membrane compatibility. Third, discharges of residual chlorine into the environment are now known to be harmful due to its high reactivity, which results in the formation of toxic and potentially carcinogenic chlorinated disinfection byproducts (e g, trihalomethanes, haloacetic acids). Conversely, residual hydrogen peroxide readily autodecomposes to environmentally benign water and oxygen.
Consequently, there is substantial need in the art for the efficient production of hydrogen peroxide, on site, at low concentrations, and at low cost.